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VOC e missions and trends in Los Angeles basin

VOC e missions and trends in Los Angeles basin. Agnès Borbon 1,2,3 , Jessica B. Gilman 2,3 , William C. Kuster 2 , Stuart McKeen 2,3 , John S. Holloway 2,3 , Carsten Warneke 2,3 , Joost de Gouw 2,3 1. LISA, CNRS, University of Paris Est-Créteil and Paris-Diderot, Créteil, France

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VOC e missions and trends in Los Angeles basin

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  1. VOC emissions and trends in Los Angeles basin Agnès Borbon1,2,3, Jessica B. Gilman2,3, William C. Kuster2, Stuart McKeen2,3, John S. Holloway2,3, Carsten Warneke2,3, Joost de Gouw2,3 1. LISA, CNRS, Universityof Paris Est-Créteil and Paris-Diderot, Créteil, France 2. Chemical Sciences Division, ESRL, NOAA, Boulder, Colorado, USA. 3. CIRES, University of Colorado, Boulder, Colorado, USA. CalNex workshop – May 16th 2011 – Sacramento, CA - USA

  2. Outline • Motivation and data • Determination of urban emission ratios • Week-end vs week-day • Preliminary comparison with inventories • Summary

  3. Motivation and data How can we improve the emissions inventory for greenhouse gases, ozone and aerosol precursors (extracted from CalNex White Paper - Jan. 2008) A first step : evaluation of the emission inventory Target species : VOC emission inventory observations [VOC]/[tracer] QVOC/Qtracer Detailed VOC composition - CalNex 2010 at Pasadena Hourly emissions of major regulated and non regulated pollutants : - NEI (national) – 2005/dec.2008 - CARB (regional) - 2008

  4. Night 1-2 m.sec-1 Mid-day LA plume transport Pasadena groundsite GC-MS instrument (Gilman, 2010) C2-C11 NMHC, C6-C9 aromatics, OVOC, DMS 30-min time resolution 0.5 m.sec-1

  5. Observations : diurnal profiles primary secondary signature of primary emissions, mixing and chemistry Ox CO need to define a set of ‘no-chemistry’ conditions to determine urban ER acetaldehyde acetylene benzaldehyde 1,2,4-trimethylbenzene

  6. Enhancement ratios VOC/CO (or C2H2) benzene m+p-xylenes acetaldehyde Photochemical depletion + Photochemical production Emission + Photochemical age (Calvert, 1976) :

  7. Methods to estimate urban ER Linear regression fit method (LRF) from nightime data (22:00 – 06:00) when t < 1 h Photochemical age method (OH) (de Gouw, 2005 ; Warneke, 2007) benzene benzene [VOC]/[C2H2] m+p-xylenes m+p-xylenes see also de Gouw’s poster on Tuesday [VOC]/[C2H2] photochemical age (h) acetylene ppb

  8. Linear regression fit method (LRF) R2 > 85% Alkanes >C4 Aromatics Alkenes Aldehydes acetaldehyde ethylene 60% < R2 < 80% C2-C4 alkanes Ketones Alcohols n-butane methy ethyl ketone  dominant anthropogenic origin at night

  9. Estimation of urban ER from LRF ER of 42 VOC ppt/ppb CO ppt/ppb CO

  10. Performance • for primary anthropogenic VOCs ER (C2H2) comparison Relative difference vs rate coefficient 1:1 +20% linear regression fit (ER photochem – ER LRF / ER LRF ) (%) - 20% photochemical age fit kOH (cm3.molecules-1.sec-1) short-lived long-lived • relative difference  ± 20% • very good agreement

  11. Trends : LA vs Boston/NYC-2004 VOC/C2H2 ethanol slope : 0.94 ± 0.06 R2 = 0.91 very good agreement except for ethanol (biofuel additive to gasoline) LA - 2010 Boston/NYC - 2004

  12. Week-end vs week-days diesel-fueled vehicle exhaust related undecane acetaldehyde abundances constant no statistical differences between slopes (t-test ;  = 5%) •  observed VOC and CO emissions are driven by gasoline-fueled LD vehicles • no weekend-weekday effect from the inventory either

  13. Evaluation of emission inventories • preliminary • 2 grids : great LA and Pasadena area

  14. Evaluation of emission inventory : NEI ER (VOC/CO) Consistency for aromatics  vehicle exhaust origin Large discrepancies for other VOC tracer : acetylene alkenes < propane < oxygenates  area source contribution for alkanes and oxygenates NEI - 2005 CalNex - 2010

  15. CARB-2008 vs NEI-2005 Hourly emissions of CO 3 non-lumped species : ethylene, xylenes, methanol inventory Hourly trafic counts CalNex - 2010 PeMS network

  16. Summary • Determination of urban emission ratios : • ER derived for 42 VOCs at ± 20%  efficiency of both independent approaches. • ER consistent with previous datasets. • Weekend vs weekday : • No weekend effect at the groundsite  gasoline vehicle exhaust emissions dominate VOC composition (at least observed ones). • Preliminary evaluation of emission inventory : • Large discrepancies with NEI (overestimation of CO emissions). Consistent previous studies. • Emission ratios with CARB-2008 seem to agree better

  17. Thank you !

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